One of the most critical issues the United States faces today is preventing terrorists from smuggling nuclear weapons into its ports. To this end, the U.S. Security and Accountability for Every Port Act mandates all overseas cargo containers be scanned for possible nuclear materials or weapons. Detecting neutron signals is an effective method to identify nuclear weapons and special nuclear materials. Helium-3 gas is used within detectors deployed in ports for this purpose.
The catch? While helium-3 gas works well for neutron detection, it’s extremely rare on Earth. Intense demand for helium-3 gas detectors has nearly depleted the supply, most of which was generated during the period of nuclear weapons production of the past 50 years. It isn’t easy to reproduce, and the scarcity of helium-3 gas has caused its cost to skyrocket – making it impossible to deploy enough neutron detectors to fulfill the requirement to scan all incoming overseas cargo containers.
Helium-4 is a more abundant form of helium gas, which is much less expensive, but can’t be used for neutron detection because it doesn’t interact with neutrons. However, A group of Texas Tech researchers, led by Horn professors Hongxing Jiang and Jingyu Lin, have developed an alternative material – hexagonal boron nitride semiconductors – for neutron detection. This material fulfills many key requirements for helium gas detector replacements and can serve as a low-cost alternative in the future.
By using a 43-micron-thick hexagonal boron-10 enriched nitride layer, the group created a thermal neutron detector with 51.4 percent detection efficiency, which is a record high for semiconductor thermal neutron detectors.
“Higher detection efficiency is anticipated by further increasing the material thickness and improving materials quality,” explained Jiang, a Horn professor, the Edward E. Whitacre Jr. Chair in Electrical & Computer Engineering and a co-director of the Texas Tech Nanophotonics Center. “Our approach of using hexagonal boron nitride semiconductors for neutron detection centers on the fact that its boron-10 isotope has a very large interaction probability with thermal neutrons,” Jiang continued. “This makes it possible to create high-efficiency neutron detectors with relatively thin hexagonal boron nitride layers. And the very large energy bandgap of this semiconductor – 6.5 eV – gives these detectors inherently low leakage current densities.”
The key significance of the group’s work? This is a completely new material and technology that offers many advantages. “Compared to helium gas detectors, boron nitride technology improves the performance of neutron detectors in terms of efficiency, sensitivity, ruggedness, versatile form factor, compactness, lightweight, no pressurization … and it’s inexpensive,” Jiang said. This means the material has the potential to revolutionize neutron detector technologies.